Today, data storage technology is based on three main physical characteristics of materials, namely electrical, optical and magnetic. Flash memory based on the principle of charge storing in a simple capacitor, DVD coded with the change of reflectivity in optical wavelengths, hard disc coding data with regional orientation of magnetic thin films can be given as examples. Even though these technologies are used commonly, they have physical limitations specific to themselves in terms of scalability which is a precondition for the increase in data storage density. New and emerging technologies are considered for high density, low power consumption devices especially for use with battery operated mobile devices. Low manufacturing costs and high read/write speeds also drive the research towards an optimal memory device that can replace or can be used with current technologies. Even though there are strong alternatives such as Phase-Change Memory (PCM) and magnetic-random access memory (MRAM), search for denser, faster and power efficient devices still continues [1,2].
Recent developments in spintronics research gave way to a variety of inventions in magnetic recording which offer Non-Volatile (NV) storage capability and durability. Current technology, the magnetic hard disc drive, is limited in scalability due to the super-paramagnetic effect (limits the cell size) and is bound to moving components to store and read information such as rotating discs and moving read/write-heads which increase the device size and consume too much power. Utilization of spin polarized electrons in spin-transfer—torque MRAMs or STT-RAMS overcomes the problem of high power consumption by switching the magnetization of the bits via spin polarized currents which eliminates the need for moving parts. The scalability issue in magnetic memory can be addressed by utilization of the third dimension in three-dimensional (3D) memory structures which either consist of layers of magnetic information [3] or make use of the volume inside the memory as in racetrack memory design [4]. Such memory devices utilize spin transfer torque [5], heat assisted stray field induced magnetization switching [6], opto-magnetic methods [7].
Disadvantages of known memory devices can be summarized as follows;
Current memory technologies such as flash memory, DVD and hard disc drives are limited in scalability and fall short in answering the demand for higher storage capacities. These memory types face issues as they are scaled down such as charge leakage in Flash memory cells, wavelength limit in DVDs and superparamagnetic effect in hard disc drives.
Moving parts inside the memory devices also limits the size, consume too much power and can malfunction causing mechanical problems.
Current technologies have read/write times on the order of milli-micro seconds. In discs with moving parts, the speed is limited by the rotation speed and/or the speed of read/write heads.
Some of the current memory technologies such as DRAM are volatile. Therefore they require power consumption to refresh the memory.
Long term stability of the binary states is an issue for some technologies such as PCM.
The requirement of separate reader/writer/buffer units not only complicate the device structure, but also increase the manufacturing costs in some technologies such as hard-disc drives. In some emerging three dimensional (3D) memory technologies such as race-track memory and opto-magnetic memory bit transfer is required in order to read which increases the error rate and costs extra time.
So a novel 3D non-volatile memory design with ultra-high density, no moving parts, individual bit access hence nano-second read/write times, stable logic states and reduced manufacturing costs by incorporating reader and writer units into the design is needed.